Cheat Sheet: What is a 'PDS' — the most extreme fire weather warning that's issued again for this week

The National Weather Service uses a number of shorthands to warn the public of adverse fire weather conditions.

For example, we've been hearing a lot about red flag warnings — a combination of heat, winds and low humidity that could lead to bad fires.

• Read all about red flag warnings here

Now, another in a recent series of PDS, or a "particularly dangerous situation" alerts has been issued for this week, starting at noon Monday (Jan. 20) through Tuesday (Jan. 21) morning.

So what is it?

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What is a "particularly dangerous situation" alert?

Areas expected to be most impacted by dangerous winds starting on Tuesday.

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National Weather Service

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Think of it as the Olympic gold of fire weather warnings, says National Weather Service meteorologist Ryan Kittell.

Kittell said the "PDS" label was already in use by the National Weather Service to describe other weather hazards.

In October 2020, the weather service started adopting it for fire conditions. Two months later, the second one was issued.

In 2020, "when we saw just an extreme red flag events — damaging winds, extremely low humidities," Kittell said. "We just felt the need to try to message that this is a red flag warning for sure, but the upper echelon, upper tier of what could happen."

In other words, says fellow NWS meteorologist Rose Schoenfeld, "this tagline is one of the loudest ways that we can shout."

What are the criteria?

The weather service issues this super duper rare fire weather alert under these weather conditions:

• Single digit relative humidity
• Sustained winds of 35 mph or greater and/or gusts 60 mph or greater
• Very dry vegetation — live fuel moistures less than 60%; dead fuel moisture less than 7%

Conditions that could lead to a high risk of:

• Extreme fire behavior and very rapid growth
• Many downed trees
• Power outages and Public Safety Power Shutoffs

How often is it issued?

They are rare, but the PDS red flag warning has already been issued three other times in as many months — an indication of the kind of extreme weathers Southern California has faced of late.

Specifically, the nearly 20,000-acre Mountain Fire in Ventura County in November and the Franklin Fire in Malibu in December.

And of course, it was issued last week for the historic Santa Ana windstorm behind the Palisades and Eaton fires that are still currently burning across Los Angeles County.

The weather service says the PDS for peak winds this week, however, won't be as severe.

"This is not going to be as strong as last week's historical windstorm," Schoenfeld said.

Fire resources and tips

If you have to evacuate

• Cheat sheet: Your very short guide to getting packed up right now to evacuate
• Cheat sheet: A very short guide for how to leave your house if you need to evacuate
  

If you have more time:

• Every day is now fire season. Let's get you ready for the next wildfire burning near you

Things to consider:

• Evacuation terms can be confusing. Here’s what they mean and how to sign up for alerts
• This is why fire officials don't want you to stay and defend your home

Navigating fire conditions

• Cheat sheet: Your very short guide to driving in high winds and fire danger
• High winds and fires mean power outages. Here's how to prep

How to help yourself and others

• Resources for SoCal fire victims, evacuees and first responders
• What to do — and not do — when you get home after a wildfire
• If you want to help fire victims, resist the urge to volunteer
• These are the steps fire victims need to take to make an insurance claim

Understanding how it got this bad

• Yes, wildfires are getting worse. The history that got us to this moment